Q345D钢中含钙类夹杂物的演变和生成机理分析

Analysis of evolution and formation mechanism of calcium-containing inclusions of Q345D steel

通过工业实践研究Q345D钢生产过程含钙类夹杂物的演变和生成机理,并结合热力学计算研究了夹杂物凝固过程的转变机理。结果表明,钢中钙主要来源于VD真空冶炼和钙处理;真空前夹杂物CaO含量很低,破空后夹杂物CaO含量开始升高;之后由于钙处理,夹杂物CaO含量进一步升高。钢液冷却凝固过程中夹杂物发生明显转变,铸坯夹杂物中CaO含量明显降低,CaS含量显著升高,其结果与FactSage热力学计算结果一致。铸坯大尺寸含钙夹杂物主要分为钙铝酸盐、CaS包裹钙铝酸盐、CaS包裹钙铝酸盐且中间析出尖晶石、CaS和Al2O3黏结型及CaS和尖晶石黏结型;统计表明,铸坯中夹杂物尺寸越大,夹杂物中CaO含量越高,大尺寸夹杂物中CaS含量极低。

The formation mechanism of calcium-containing inclusions during the production of Q345D steel was investigated through industrial trials.Thermodynamic calculations are used to study the transformation mechanism of inclusions during solidification.The results showed that calcium in steel mainly comes from the VD vacuum and calcium treatment.The CaO content of inclusions before the vacuum is very low.However,after the vacuum break,the CaO content of inclusions increased due to entrainment.After calcium treatment,the CaO content of inclusions further increased.The composition of the inclusions changed significantly during solidification.The content of CaO in inclusions of slab decreased significantly,and the content of CaS increased significantly,which is consistent with the thermodynamic calculation results.The large-sized calcium-containing inclusions in the slab are mainly divided into calcium aluminate,calcium aluminate surrounded by CaS,calcium aluminate with spinel surrounded by CaS,CaS,and Al2O3 bonding type,and CaS and spinel bonding type.The larger the inclusion size is,the higher the content of CaO is.The content of CaS in large-size inclusions is extremely low.